Light control



K. BERNIIQGER arm. 2,472,741

LIGHT CONTROL Julie 7, 1949.

Filed April 16, 1947 mvENTORs 7w .L. BEEN/M6516 01W uA/ EYA. LoweEY ATTORNEYS Patented June 7, 1949 UNITED S TAT ES PATENT OFFICE LIGHT CONTROL Kenneth L. Berningerand ChaunceyH. Lowrey, Dayton, hlo,'assign0rs to The *Eld'eeProducts Company, Dayton, Ohio, a corporation of Ohio .ApplicationApril 16, 1947, .Serial .No. 341,176

12 Claims. '1

This invention relates to the control of electric circuits where th manifestation of the work circuit is desired to continue'for a predetermined period of time after a control circuit is selectively energized.

One object of the invention is to; so control an electric circuit that a predetermined elapse oftime ensues before any 'apparentchangein the circuit .takes place.

More specifically, an object of the invention is to control a lightcircuitsuch-thatit is instantaneously energized in response to apremeditated act of an attendant. and thereafter automatically deen'ergizes afterthe' elapse of a predetermined periOd.

Another Object of the invention is to control a flood-light posted at the entrance of'a residence garage or the like so that a single operation of .the controlling switch will energize the light circuit which will continue over a sufficient period of time 'to'permit a person to leave the car, open the garage doors, drive the car in the garage, condition the car for the night, and retreat to'the living quarters, beforethe light circuit is automatically deenergized.

Still another .object of the invention is 'toprovide an electric switching unit that will hold a circuit closed for a selected period of time after and following an initial current passage.

Yet another object of the invention is to provide an automati'cswitching unit for automatically deenergizing either circuit branch of a two point remotely control-led'light circuit upon the elapse of 'a predetermined period of time after the respective branch is energized from either one ofthe two'points of remote'control.

Another "object of the invention is to provide a circuit controlling unit of the suspended or delayed action type that may be plugged into an existing, light installation without forfeiting any of thefeatures of the original installation of said light.

Another object of the invention is to provide a delayed-action circuitcontroller of'the unit type that is connectible 'intoan electric circuit fitted with manual switches without disrupting or-disorganizing the control of the circuit by said switch, and in which 'said controller provides'for instantaneous closing of the circuit with timed opening of said circuit after a single manipulationcby an actuator of said unit, the unit also having means embodied therein for by-passing its operation from-a remote or other point.

The foregoing objects and advantages are accomplished by providing a unitary construction 2 that is'tapped into an existing electric circuit to be controlled, and which gainsitsenergy from the taps so made. A transformer whose primary is in the circuit to be-controlled'develops energy in the secondary to which is connected a primary actuator switch-fin;circuit-with a coilwinding in attractive relation to an armature whose movement'controls -a snap-action switch across the lines to the device to "be controlled, held in circuit closed position for-a predetermined period of time 'by "a restraining device energized 'bythe flow-of current 'to the device in the circuit to be controlled. More specifically, to a work circuit, suchas aflood-light connected to a-currentsource through :a; manual switch for controlling the flood light, there is connected a controller unit embodying a control circuit and an impulse circuit. Thecontrol circuit is shunted across theprimary of a step-down transformer connected to the work circuit at the terminals of the original control switch, and the shunt includes a heater element in series with a "normally open snap switch actuated by an armature of an electric relay in the impulse'circuit. The impulsecircuit includes the secondary ofthe step-down transformer, the winding of =the'-'electricrelay, an offon switch'and a-pneumatic' switch actuated by 'a drive-way actuator. The impulse circuit onbeing closed, even momentarily, energizes the winding of the relay that actuatesan armature or lever to. close the snap switch which'closes the work circuit; and a, bi-metal'detent exposed'to a heatingcoilspringsinto place to-holdthe snap switch in circuit ;closing;position,while the flow of current in the heating coil-efiects retraction of the bi metal-detent to permit opening of the work circuit after a measured interval of time.

Further "obj ects and advantages of'the present invention will beapparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the-drawings:

Fig. 1,'is acircuit diagramof the control unit applied to a workclrcuit having a single point of control.

Fig.2 is a circuit diagram of a control unit suitable for -a work -circuit normally controlled from two remote points.

Figs.'3 is a fragmentary-view'showing parts in a moved position.

Fig. '4 is a fragmentary view I of a modification, by'whicli a single transformeris-substituted for thedoubletransformershown-in'Fig. 2.

Whilethe improved system is adapted to the control of various kinds of work circuits under widely varying conditions, it is especially adapted for and will be described herein as applied to the control of a flood-light for residence garage lighting. It is to be understood, however, that it is not intended to limit the invention to such disclosure nor to the particular construction of the unit, but it is aimed to cover all modifications, alternative constructions and uses falling within the spirit and scope of the invention as expressed in the appended claims.

With particular reference to the drawings, and I2 indicate the line conductors of a power supply or current source attached to a wall switch I4 for the control of a flood or yard light i6 as in the usual installation. Such installations are usually found on the larger estates or residences, and serve to light the approach to a garage when turned on. They are customarily needed but for a short duration of time, five minutes for example, or long enough for the driver of a vehicle to get out from the same, open the garage doors, get in the car and drive it into the garage, close the garage doors and leave the garage. Nearly half of the time, the lighted lamp will be forgotten, particularly if it is an installation of the two-way or remote control type. The herein described control unit will take care of the matter and automatically turn the light on as the vehicle approaches the garage, and turn off the light after a measured interval of time, if it is forgotten.

The control unit is provided with a cable containing the necessary conductors l8 and for attaching to the terminals 22 and 24 of the original light switch l4, so that a primary winding 26 of a step-down transformer 28 is in series with the lamp IS. The cable is generally indicated by the dashed circle 30 and may be of any concontact 86 connected by lead 88 to the other end venient length to extend from the wall switch l4 to a position selected for the installation of the control unit which may be attached to the wall near the wall switch, or at a point near the garage door opening.

In any event, the control unit embodies a control circuit for the work circuit, to include a lead 32 joined to the conductor 20 and the terminal 34 of a normally open snap switch 36 whose other terminal 49 is connected to a lead 42 that connects to a terminal post 4-4 of a heater element composed of a heater coil 45 trained about a bimetal blade 48 and thence connected to a binding post 50 from which extends a lead 52 joining the conductor I8 of the cable 30. Thus, the control circuit is shunted across the primary of the transformer and is continuously in communication with the power supply lines It and 12 except for the normally open switch 36.

Pivoted near the snap switch 36, so as to be I in engaging relation with an actuating pin 54 thereof, there is a leaf member 56 that is free to turn about a pivot pin 58, the free end of which leaf is disposed over the end of a core 50 of an electromagnet, and intermediate of which leaf there is a riser 62. The riser is of such dimension and is so positioned with respect to the bi-metal blade 48 that the free end of the blade 48 may engage either the body of the leaf 56 or may flex to that position in which the riser is interposed between the leaf 56 and the free end of the blade 48 as shown in Fig. 3. The blade 43, responding to a predetermined change in temperature effected by the heating coil 46 may take up either position. Toward that end, the blade is attached at one end to a bracket 64 which is fixed to a of the secondary 10, of the transformer 28. The contact points 84 and 86 constitute the elements of an impulse switch involving a diaphragm 85 over a chamber 8'! that is subject to the change of air pressure within a hose element 89 that may be laid over the path of vehicle movement so that treading or depression of the hose will actuate the diaphragm 85 to close the contacts 84 and 86.

Such action, that is treading on the hose closes the electrical path through the secondary of the transformer, which now becomes energized and current thereupon flows through the relay winding 16 if the master switch 82 is closed. The unit, to provide for full adaptability under all conditions, is also provided with a normally open manual impulse switch 90 shunted across the switch 85, to connect with the leads 80 and 88, as is also a pair of binding posts 92 and 94 having leads 96 and 98 connected with the leads 80 and 88 respectively. By those means, the control unit can be set into operation at the control unit by closing the manual switch 90, or by closing of a pendant or like switch attached to proper leads and connected from a remote point to the terminal posts 92 and 94.

In any event, closing of either of the switches at 84, 8B or at 90, or at 92, 94, the result is the same. Even a momentary closing of the impulse circuit at any one of these points energizes the winding '16 that actuates the leaf 56. That is because the transformer 28 is one of the stepdown type in which no substantial current flows in the primary 25 until a circuit is closed through the secondary 10. When the winding 16 is energized the core 68 is drawn up with such force as to strike the leak 56 and push it upward enough that the actuating pin 54 of the switch efiects closing of the switch 36, and allows the bi-metal member 48 to flex to the position shown in Fig. 3 where the end of the member engages the under side of the riser 62 to hold the switch closed until the member 48 reflexes under the rise of temperature effected by closing of the control circuit to disengage the riser. When the leaf member 55 is moved to depress the actuating pin 54, a circuit is closed through the snap switch 36 in the control circuit which by-passes the primary 26 of the transformer and energizes the lamp IE5 or other work circuit connected therewith. The heater winding 48 is also energized by closing of the snap switch 36. A transformer of the bell-ringing type is preferred, or one similar T thereto in which the primary is so constituted that though continuously connected to the source its primary 26 in series with the work element ofiers too much resistance to permit full manifestation of the work device. Consequently the light 16 or other work device is not energized, because of the high impedance in the primary 26, until the same is by-passed or shunted by a lesse resistance path, here constituting the control circuit. The resistance thru the contact circuit including the heater coil 46, is relatively low as comparediwith that throughtheprimary of the transformer; andofirs no substantial ob'strucz-v tion'" to the full manifestation of thel'amp lfi 'or other work device.

At the instance of closing the impulse circuit and" actuation ofthe leaf 56* the heating coil 46 cold and immediately flexes to:;'aaposition with.= itsfree end beneath the riserlil' carried' by" the leaf 56$ With'the opening of theimpulse 'circuitat any point the leaf may now drop back so that the riser GZ' engageSthe end -of the bimetal member 48 which holds the actuating pin 54 far enough depressed to maintain the snap switch -35cl'dsed. so lo'n gas" the snap switch is= closed" the source current 'flowsthrough-the" heater coil 46* which after a-*- measured length of time causes the bi-metal member to reflex to a positiorrto one sideof the riser B'Twhich now fully retracts toitsrest positionand thereby 'opens the control circuit; Opening of' 'thecontrol cincuit' reinserts the primary 2'6 'into the work cir-'- cuit 'so that -th'e-light'=- It or similar work device becomes insufficiently energized to function. Thus, with only a momentary-closing of the impulse circuit the'work device is' energized'whi'ch .1;

continues to operate for 'a" predetermined" period of time and'then automatically becomes deenergized.. Asa practical example, the 'heating coil and lei-metal element are so-chosengmountedand' adjusted, that the control circuit is" opened about fi've minutes-after the 'closing of the impul'se'cir: cuit. Either a longeror a shorter period of time maybe selected and provided for tosuit' other selectedconditionsof operation.

In 'the'sch'eme of Fig; 1-; the'snap action switch l 36' is mounted on the b'ase fili' by the screw'de'viccs 31'whil'e the coil' 'winding IS- encircles the core fifl having'a' bracket fi-l mounted'on the-base 5twhlch constitutesan electromagnet set inattractive relation to the movable armature or core" 513' fonactuating the leafifi: Thus, when the coil 16is energized; the core is attracted and the snap" switch closed.

IncFign. 1; there is shownrasystem'for the autm matic: control 'ofc'a work circuitthat :is normallycontrolled by a single manual switch, such. as'th'e" usual wall switch" Mi All of the element'sof the control unit: areimounted on a: single base board 66 and terminateat onelpoint-inza cablezfill having? the leads l8 and 20 ready: for: attachmentnto the terminals-22 and 24 .of the wall switch, anditer: minatingflatranother point. in la flexible hose: 89' that maybe laid out on-the drive-way in the path .of thevehicle tobe driven intolthe garage;

In-Fig; 2, a similar adaptationtismade for;the

type or workcircuitnormally'controlledi. from: either one of two :remotely separated. points There the-lineconductor IU of the work" circuit connectswiththe wor-lc deviceor lamp [G and thenceto; theiswitchpoint 22 to. which. is :coh I nected the. switch It that'isshere selectively-1 en;- gageable :withthe. switchpo-ints li a-andl3 from. which extend the branches l5 and IT respective ly j,oining-posts l9 and-2i respectively selectively:

engageable. by a switch memberv2'3 pivoted atzh':

to which-is connectedrtheother line conductor? 2.1 connectedrwithlthe currentsource; The-usual: practice is in the caserof a garage lightto'mount-x one of the.- switches M and 23 inithe garagezand the-other at I the: entrance door .ofthesresidence',. so that by manipulating. the. switch:- :in nearest proximity, the lamp I6 may bGfJ-Bithfillifihte'id or extinguished The control. unit for. the two point control: workl. circuit embodies-the same-l principles.- but plis'h this; one end of both primaries'is jointedto' the leads I ttwhichl" becomes a commonlead for both, and :thedead tli -joinsone'end of bothsecon'daries Hl and I10; the secondary l0 be ingz connected: into :the impulse circuit substan tiallyeasrhas: been described, while the secondary l'wi'is connected" into the impulse circuit in I at similanmanneriby extension of certain conned--- tionsrasawill beidescrib'eda A lea'd l'iit connectsz': thfio'bhiel end-: :of:.:secondary I'll] to post l'l l andi thencei'through'"coil "IT5:to post l'l's from which: lead ilfiillnun's-z tofsioin'f the lead 88 'connecting ther master; switch- 182. a-nd icontact fit' of the impulse switch; Disposed adjacent the" coil Ht islltheleaf lfilizfor: "actuating the snap switch l36 -t'o 1 close the :controlecircuit including the lead: i 32 ext'ending :fromf iit'hand'i the lead I42 connecting "T with the; heatinga; coil Mt and thence by' lead I l52back to; theflirie E20 and to the post I 32" The leaf l56 carries the riser I62 so positioned tha't it" is disposedf'overithe endof the bi-metal member M83 when'theleaf is first actuated by thecoil. I T5 inv a manner'similarto theacti'oni ofa the leaf 56 and bi-metal member 581 In" 2;. the work circuit may be manually" contfiolledz; by; either original switch. It may be: turned; ons-at either switch mm 23'and left onas long" as desired; or thecircuit' may be opened: at theis'a'me point or: at the other point; When the-manual control switches ofthe= orig'-- inal installation are both ofi, the .work' circuit may beclo'sed and automatically opened By" use" of the controlidevice," from eitherof' three points; that is; theipneumatically operated switch 85, orthe. manual contacts 9t"; or yet theremote controliswitch" connected at 92 and M: The position off-the: switches l4 and 23,-if the master switch"82-.Iisi'v closed; will determine which" of the relay'devices willbecome efiective. When either of. therelay devices become effective, the work: circuit- 1 will be immediately energized and after the elapse ot a measured period of time Will -be deenergized automatically by the controlv unit. With thelamp l6 off and'the switches l4 and 23-tbot-h in the: open: position asshown" in Fig; 2; and". in engagement with" the posts it, El respectivelyxthe primary 26 of the-trans former:v HZBr is connectedin: series with the work. device lfiand thezrelays device-116, let 'becomes efiective. withfa momentary closing of either of therswithhes 85, 80,; or the rem'ote control lllle- 'JL'hIatJ -wcircuitLbeing:v closed; the; leaf- 156 is actuated to close snap switch I 36 which in turn energizes the control circuit that extends from the conductor I 8 through 32 and 132 to the switch I36 and thence by lead I42 to the heater winding I46 and returning through leads I52, and I20 to post !3. Thus, the work circult is energized and the lamp I6 is lighted, with current flowing through the heater coil to actuate the bi-metal blade I48 which after a measured interval of time allows the snap switch to open.

In Fig. 4 there is shown an adaptation by which a single transformer 28 serves to supply power for either branch of the double control point circuit shown in Fig. 2. It diifers from the other circuits principally in that the winding 26 of the transformer has the opposite ends not only connected to the lines 32 and 52 as in Fig. 1, but also has those ends connected to theswitch terminals l I and 53 as in Fig. 2, while the work device It is connected to the switch point 22 as in Fig. 2. With the switches I4 and 23 in the off positions shown, there is no glow of the lamp due to the characteristics of the circuit as has been explained. However, upon closing of an impulse switch, the control circuit is completed so that current in the line 2'! follows through 25, 23, I9, I5, II, 20, 32, to the snap switch 36, which being closed completes a circuit back to the lamp I6 by way of leads 52, I8, I3, I4, 22, and I0. By that means a single transformer serves the purpose of control for the lamp I6 in either off positions of the switches I4 and 23.

From the foregoing it should be seen that the work circuit may be controlled by the control switch of original installation without hindrance from the automatic control unit that has been attached thereto. That means that the original installation has not been deprived of any of its features by the installation of the additional control unit. On the contrary, the control has been greatly augmented because with it the light can be turned on at any one of several points by momentary closing of one of the impulse switches, and. the unit will see to it that the light is turned on again after a measured interval of time. As a further xample, the person may momentarily close the switch 90 and then open the garage doors, get in the car, start the engine, drive the car out of the garage, get out of the car and close the garage door, return to the car and drive away. The control unit will in due time, whatever the unit is set for, turn 01? light. The hose of unit having been laid across the path of vehicle on its return, the control unit is all set for reoperation on return of the vehicle which upon rolling over the hose gives such momentary closing of the impulse circuit that the light is turned on long enough for the vehicle to be replaced in the garage and readied for the night. As a safeguard against unintentional use of the light, such as during the daytime or while absent for an extended time, the master switch 82 is opened which interrupts all operation of the unit, but does not interfere with the manual switches of the original installation. If preferred, a switch I96 may be connected into one of the leads I 8 or 2B of Fig. 1, which will disorganize the whole unit when open, so that there is then no current impression on the transformer. A similar switch if placed in the lead I 8 to the mid point of the two primaries 26 and I 2'5 of Fig. 2 would serve a like purpose.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms {might be adopted all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a control unit for controlling a lamp circuit embodying an electric lamp and a manually controlled switch connected to a current source, the combination comprising, a transformer having a primary winding across the manual switch, a secondary winding, a control circuit including a control switch and a heating coil shunting the primary winding, an electromagnetic winding and an impulse switch serially connected with the transformer secondary, a pivoted leaf responding to the energization of said electromagnetic winding for actuating the control switch, a bimetal latch exposed to the heating coil and operable to hold the pivoted leaf in control switch closed position, and means for actuating the impulse switch for energizing the magnet and the lamp circuit although the manually operated switch is open.

2. The combination set forth in claim 1 wherein the primary of the transformer is constantly connected in series with the lamp circuit to be controlled and offers such substantial reluctance that the lamp is nonoperative, and wherein closing of the impulse switch effects shunting of the transformer primary by energizing the control circuit and substantially full energizing of the lamp circuit.

3. The combination set forth in claim 1 wherein the transformer is of the step-down type and has a primary winding serially connected with the source and the lamp circuit, and whose ,secondary winding must be in circuit completed condition before energy will fiow in the control circuit to by-pass the primary winding and energize the lamp circuit.

1-. In a conventional lighting circuit embodying an electric lamp and a pair of control switches permanently connected to a current source for energizing the lamp from either of two more or less remote points, a control unit adapted to be connected to one of the switches for predetermined control of the lamp circuit while the control switches are both open and comprising in combination, a pair of current transformers having primary windings connected in series, means connecting the primaries with one of the control switches so that one or the other primary will always be connected in series with the electric lamp when both of the control switches are open, a secondary winding for each transformer, a solenoid connected with each secondary, a common return for both solenoids and an impulse switch connecting the common return to both of the secondaries, a pair of control circuits connected to the lighting circuit in parallel with the primaries, each control circuit including a normally open snap action switch associated with each a solenoid, and time restoring latch means for holding the control switch closed for a predetermined period of time, said impulse switch when closed completing a circuit through the secondary and solenoid whose primary is then in series with the electric lamp, whereby, the associated snap switch closes the respective control circuit to shunt the serially connected primary and give full energization to the electric lamp of the lighting circuit.

5. In a conventional lamp circuit embodying an electric lamp device and control switch permanently connected to a current source, a control former havinglaprimary constantly impressed .with the potential of V .the sourcena snap.v control .switchland a heating. device in :series connected across-the:, trarisformer. .primaryland adapted ,to

qenergizetthellamp. ,device whcmthe snap ,switc is. closed-ran actuatingumembersfor closing the snap switch, an electromagnetic device for moving the actuating member, a time controlled means including said heating device for retaining the snap switch closed for a predetermined period of time and means including the secondary of said transformer for energizing said electromagnetic device to selectively close the snap switch whereby a single manual manipulation of the control unit energizes the lamp device and automatically deenergizes the same after a selected time interval.

6. The combination set forth in claim wherein the means for energizing the electromagnetic device include a plurality of impulse switches for connecting the transformer secondary with said device and wherein one of said impulse switches is a pneumatic pouch and air column adapted to be distorted for deflecting the pouch.

7. In a conventional lamp circuit embodying an electric lamp device and control switch permanently connected to a current source, a control unit adapted to be connected to the control switch for predetermined control of the lamp circuit, and comprising in combination, a current transformer having a primary winding connected across the control switch to be serially connected with the lamp device when the control switch is open, a control circuit including a normally open snap action switch and heating coil serially connected and joining the lamp circuit in parallel with the transformer primary, an actuating leaf for the snap action switch, a bimetal latch associated with the heating coil and actuating leaf for controlling the length of time the snap action switch remains closed, and manually operated means energized by the transformer secondary for moving the actuating leaf to close the snap action switch.

8. In a conventional lamp circuit embodying two remote controlling switches for energizing and deenergizing the lamp circuit manually, the combination of means for energizing the lamp circuit upon the occurrence of a predetermined event though the two remote controlling switches remain open, and means for automatically opening the lamp circuit at a measured interval of time after the lamp circuit is energized, means for taking energy from the lamp circuit including a current transformer having a primary winding connected to one of the remote controlling switches so as to be in circuit completing connection with the lamp circuit whenever both of the remote controlling switches are open, a control circuit shunting the transformer primary and including a snap action switch and heater element in series so as to be energized by the lamp circuit and by-pass the primary whenever the snap action switch is closed, lever means for closing the snap action switch, a bimetal latch for holding the lever in switch closed position, said latch being automatically responsive to the heater element for releasing the lever to the switch open position, and means actuated by current from the transformer secondary for selectively actuating the lever means, whereby the negli e c p iav p ede e fei n -,rs1. ffee sill e s le t-9 .ihe am .e rtg m sh-W twitc e ar be he sa meet n se o th F n 4 laim l so), l wherein the ,means for energiz ng ,the lamp cirouit operates equally, fiec tively whether'the two m le qoni ll ngswxle se in one Off Position orinthe otheroff position.

10. In the conventional lam'p circuit embodying two remote contr olli ng switches for energizing ari r eene s in .ihelaning rsu i ma u the combination of meansfor energizing the lamp circuit upon the occurrence of a predetermined event though the two remote controlling switches remain open, and means for automatically opening the lamp circuit at a measured interval of time after the lamp circuit is energized, said means for energizing and automatically opening the lamp circuit comprising a compact unit electrically connected across one of the two remote controlling switches, and includes transformer means having a primary winding impressed with the current of the lamp circuit and adapted to develop energy in a secondary winding, means connecting the automatic circuit opening means with the primary winding means of the transformer, and impulse actuating switches for effecting actuation of the automatic means.

11. In the conventional lamp circuit embodying two remote controlling switches for energizing and deenergizing the lamp circuit manually, the combinat on of means for energizing the lamp circuit upon the occurrence of a predetermined event though the two remote controlling switches remain open, and means for automatically opening the lam-p circuit at a measured interval of time after the lamp circuit is energized, said means for energizing the lamp circuit comprising a unit attached to one of the remote controlling switches and including transformer means permanently connected into the lamp circuit for providing a source of energy for the unit, switch means connected in parallel with the primary of the transformer means for controlling the lamp circuit, and an impulse switch and electromagnet means for controlling the operation of the parallel switch means controlling the lamp circuit, said switch means in parallel operating in either position of the remote controlling switches to open the lamp circuit after a predetermined elapse of time from operating the impulse switch.

12. In the conventional lamp circuit embodying two remote controlling switches for energizing and deenergizing the lamp circuit manually, the combination of means for energizing the lamp circuit upon the occurrence of a predetermined event though the two remote controlling switches remain open, and means for automatically opening the lamp .circuit at a measured interval of time after the lamp circuit is energized, said means for automatic opening the lamp circuit being connected across the manual switches and includes a pair of transformers each having a primary winding insertible alternatively in the lamp circuit when the two remote controlling switches are both in the open circuit position and adapted to power the control unit, a pair of control circuits in parallel respectively with the primaries of said transformers and including each a snap switch of open contact type and a heating coil in series therewith, electromagnetic means in association with each snap switch and heating coil for controlling the operation of respective snap switch, and impulse switch means for momentarily closing a circuit through the electromagnetic means associated with the primary winding energized by the lamp circuit, the snap switch and heater coil therewith associated operating to open the lamp circuit after a measured interval of time after the momentary closing of the impulse switch.

KENNETH L. BERNINGER. CHAUNCEY H. LOWREY.

REFERENCES CITED The following references are of record in the file of this patent:

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